The present invention relates to rebound damping means for magnetically or electromagnetically actuated instant-return diaphragms of photographic cameras or the like.
In such diaphragms of the iris type, a slotted ring which normally holds the diaphragm blades open travels at high speed, shortly before the exposure, against a stop which can be adjusted in accordance with the aperture selected on a selection ring. The stop, which is generally controlled via a cam ring, determines the position of the slotted ring and thus the size of the effective aperture set during the exposure.
In order to achieve rapid successions of pictures, and in order to keep as short as possible the time between the diaphragm open position, when generally the light falling into the lens is measured for the determination of the exposure time, and diaphragm set position, during which no correction of the exposure time can be effected any longer, ever more rapidly closing diaphragm mechanisms are required. As a result, it becomes increasingly difficult to take up the high amount of kinetic energy of the diaphragm control mechanism upon impact against the stop.
In the known instant-return diaphragm constructions the slotted ring comes against a fixed stop which lies on the cam controlling said ring, which leads to undesired rebound effects. During the rebound the size of the diaphragm aperture is not precisely defined; the rebound time therefore increases the closing time of the instant return diaphragm.
West German unexamined patent application No. OS 2530392 describes a rebound damping mechanism in which contacting parts of the slotted ring and of the stop consist of magnetic material and thus adhere to each other upon impact. In this way, to be sure, rebound is avoided but a relatively large amount of force is required in order to separate the two parts for the next operation.